My Dad dealt with an Appy stud back in the 70s that was like that too. He'd been so spoiled by the "halter trainer" the owners sent him to as a yearling that he was vicious and dangerous (trainer would let him chew on whatever he wanted to keep him still during halter classes. They often had to get a new lead every show because the horse would eat all the leather off of it). Then, whenever you didn't do exactly what he wanted, he would turn on you; biting, pawing, charging, stomping, kicking, etc.
They expected my Dad to train this horse to ride...which he did (but as he says "he was young and impetuous" LOL), but it was very difficult and dangerous. He tried everything and finally had to resort to carrying a length of 3/8 inch chain whenever he was around that horse. Whenever AQ would charge, Dad would whip him to within an inch of his life with that chain. That was the only way to keep that $80K stud even somewhat manageable. There were other things done to that horse during other CTJ meetings that I won't mention here, but they were bad...very bad. BUT, Dad was the only person who could handle that horse without getting hurt, he could ride him anywhere, and he was successful in the show pen in WP, halter, team roping, and calf roping.
When my Dad left working for those folks, he warned the new trainer not to go into AQ's stall with just a buggy whip, he needed to take the chain. Well, about 3 weeks later, Dad found out that AQ had gotten the new trainer down in his stall and nearly killed him. The horse was never shown again and a few months later he was dead from a "blister beetle infestation"...which I was always suspicious of considering that he was the only horse in a barn of about 80 that got it .
But, I guess you don't get an insurance payout for shooting the dang thing because he's a lunatic.